Markoff, Falcke, Fender (ApJL): XTE J1118+480
A jet model for the broadband spectrum of XTE
J1118+480: Synchrotron emission from radio to X-rays in the Low/Hard spectral state
Sera Markoff1, Heino Falcke1, Rob Fender2
1Max-Planck-Institut für Radioastronomie, Auf den Hügel 69, D-53121 Bonn, Germany
2Astronomical Institute ``Anton Pannekoek'', University of
Observations have revealed strong evidence for powerful jets
in the Low/Hard states of black hole candidate X-ray binaries.
Correlations, both temporal and spectral, between the radio --
infrared and X-ray bands suggest that jet synchrotron as well as
inverse Compton emission could also be significantly contributing at
higher frequencies. We show here that, for reasonable assumptions
about the jet physical parameters, the broadband spectrum from radio
through X-rays can be almost entirely fit by synchrotron emission. We
explore a relatively simple model for a relativistic, adiabatically
expanding jet combined with a truncated thermal disk conjoined by an
ADAF, in the context of the recently discovered black hole binary XTE
J1118+480. In particular, the X-ray power-law emission can be
explained as optically thin synchrotron emission from a shock
acceleration region in the innermost part of the jet, with a cutoff
determined by cooling losses. For synchrotron cooling-limited particle
acceleration, the spectral cutoff is a function only of dimensionless
plasma parameters and thus should be around a ``canonical'' value for
sources with similar plasma properties. It is therefore possible that
non-thermal jet emission is important for XTE J1118+480 and possibly
other X-ray binaries in the Low/Hard state.
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